In a competitive auction, when three of the suits have been bid, a bid of the
opponent’s suit can be used to ask partner if 3NT is a suitable contract. Such
bids are called “ directional asking bids” (DAB), because you asking partner
for help in defining the final contract. The bid must be forcing since you have
no wish to play in the opponent’s suit, and asks partner to bid 3NT with a partial
stop in that suit. Qx, or J10x is considered sufficient since the player who
asks is expected to have at least a partial stop. Of course you must be aware
that your side has sufficient overall strength for the contract. Very often
you will have a definite stop in the opponent’s suit but realise that you need
extra help in the suit from partner.

The dealer opens 1
and your partner overcalls 2 ,
at your turn you bid 2
and then partner calls 3
. You have a ª stop and a good hand so 3NT would
be a good contract if your partner can help block the s,
so bid 3
(DAB)! If you had held a good stop in s
you could have bid 3NT rather than ask partner for a partial stop.

Another example: partner opens 1and
you respond 1,
and this is overcalled 2
on your left. Opener re-bids 3,
you bid 3
and now opener bids 3
(DAB) asking for help in the opponent’s suit.

If you can help bid 3NT, but if not either support one of partner’s suits or
re-bid your own suit

You must alert the DAB and explain that it is a forcing bid etc if asked. Bids
of the opponent’s suits are rarely used to show massive strength as they used
to be. Do not confuse this with an "unassuming cue bid", which is
an immediate bid of opponent's suit after partners major suit has been overcalled